A good high-definition LCD projector can still set you back US $2000, but if your wiring and woodworking skills are up to speed, you can put one together for around $600.
It’s not like you have to build it from scratch. At least two companies, DIY for Life and DIY Projector Kits, sell kits and supplies that make this something any engineer could do in a weekend.
The key items are an LCD panel and a pair of Fresnel lenses. A Fresnel lens is thin and light, made out of a piece of plastic into which concentric grooves have been cut, giving it a large aperture and short focal length. (The first Fresnel lenses were invented for lighthouses.) It doesn’t do a good job of projecting light, though, so you also need a different kind of compound lens, known as a triplet lens.
Here, the first Fresnel lens beams light from a source through the liquid-crystal display, which I’d stripped from an LCD panel. On the other side a second Fresnel focuses the image to a point on the third lens, which projects the image out onto a plane about 3 meters away.
That’s the heart of the project; the rest is just the casing. The bulb gets quite hot, so a Lexan or tempered glass heat shield is placed right before the innermost lens. A fan at the back pulls cooling air down over the LCD panel from a slit in the cover.
I bought nearly everything from DIY Projector Kits: the lenses, heat shield, high-intensity light and ballast, a thermostat to run the fan, some hardware to mount the bulb, and a set of measured plans for a generic 15-inch display-based enclosure. The entire package, including shipping, ran just under $450.
I picked up a refurbished Samsung 15-inch LCD monitor for $124 on eBay. The Samsung had been rated by DIYers as very easy to strip, and sure enough, it took me less than 30 minutes to do it. I overbought on wood, probably using about $50 worth of high-quality 2-centimeter plywood.